DAVID (Data And Voice Integration over D-WDM) is a research project sponsored by the European Community aimed at the design of an optical packet-switched network for the transport of IP traffic. The network has a two level hierarchical structure, with a backbone of optical packet routers interconnected in a mesh, and metropolitan areas served by sets of optical rings connected to the backbone through devices called Hubs. The paper focuses on nodes and Hubs architecture, and on the operations of the media access protocol to be used in the DAVID metropolitan area network. A simple access protocol for datagram (not-guaranteed) traffic is defined and its performance are examined by simulation.